In refrigeration systems which utilize compressors for compressing the refrigerant, there is a tendency for the refrigerant to become trapped in the compression chamber when the compressor is stopped and, as a result there is normally a load on the compressor motor in restarting. Where an electric motor is utilized, in order to provide for prompt restarting, it is common to add a motor starting capacitor, high torque start windings on the motor stator or other devices designed to provide the motor with high initial torque capabilities. In any event, depending on the compressor and refrigeration system, the restarting is prevented for a substantial period of time on the order of minutes. The problem is most important in refrigeration systems which operate to cool to temperatures of 40.degree. F. or below, as contrasted to air conditioning systems; because in refrigeration systems, the motor capacity is kept as low as possible to minimize cost.
Accordingly, there is a need for providing a simple and effective mechanism for restarting a refrigeration system promptly, on the order of seconds after being shut off, without the use of supplementary electrical components and without adversely affecting the efficiency of the compressor.
It has heretofore been suggested that solenoid operated valves be provided to equalize the pressure between the compression chamber and the suction chamber of the compressor. Such an arrangement necessitates costly solenoid and associated electrical controls, and results in refrigerant being entrapped in the solenoid valve inlet, commonly termed re compression volume.
It has also been heretofore suggested to provide a shallow groove in the valve plate or on the suction valve seat, between the compression chamber and the suction chamber but such a continuous bleed of refrigerant during operation of the compressor reduces the capacity of the compressor substantially.
Another prior system utilizes a combined pressure relief and unloader valve between the discharge volume and suction volume of the system. Such an arrangement has the disadvantages in that it does not unload the compression chamber, is slow to unload because of the large amount of refrigerant that must be passed through the valve to equalize the pressures, is costly, reduces capacity since it has an inherent continuous bleed even when the compressor is operating, and does not provide for an immediate restart.
Accordingly among the objects of the invention are to provide a refrigeration system which will function to permit the compressor within the refrigeration system to start immediately within seconds after being shut off and without any need for waiting for the equalization of pressures between the system's discharge and suction volumes; which system is simple, reliable, effective and low in cost; and in which involves a novel compressor unloading valve.